1. Field of the Invention
This invention concerns a filter system and its use to rejuvenate used lubricating oils.
2. Description of Related Art
The use of both single and two-stage filters for treating lubricating oils is known (see, for example, U.S. Pat. Nos. 2,302,552; 3,390,778; 3,489,676; 3,749,247; 4,886,599; and 4,977,787, and British Patents 507,065 and 836,993; the disclosures all of which are incorporated herein by reference).
However, none of these patents disclose the particular filter system and method described hereinafter.